The first practical constructed language was the south-west German Pastor Schleyer's Volapük from 1879; its complicated grammar and irregular vocabulary made learning difficult, however. The most successful has been Esperanto, devised by the Warsaw ophthalmologist Ludwig Zamenhof in 1887, that today can count some one million speakers.

It has been said that— when I made the observation, that if they were not married they ought to be—I endeavoured to stab their reputation. Now, I'll prove that I endeavoured to do nothing of the sort. [...] I'll prove it by logic, and I defy all the mathematicians in the habitable globe to known it down. I'll prove it by the regular mathematical construction of the English language, and will any man tell me there's any constructed language in the universe more mathematically regular than that?

Who does not understand, as single parts of speech, all the common combinations which serve to connect and carry on construction, such as in-consequence-of, on-this-account, [...], and the like? Indeed, we are entitled to say of ordinary common-place speakers, that as they scarcely use constructed language except in forms already existing, so, with them, each thought finds an immediate sign in some familiar sentence; but then, be it observed, the parts which compose the sign have ceased to be separately significant: the sentences so used have been brought back to the condition of original or natural language, that of exclamations, — they have ceased to be logical, by having become purely rhetorical.

What we ordinarily term language is made up of vocal signs of an arbitrary character, with corresponding written signs. As general principles are recognized in the construction and arrangement of these signs, we see at once the reason that brutes have no artificial language — that is, no sign that are agreed upon as expressive of ideas. They do indeed have a natural language, made up of natural signs, cries, and motions, which vary in different tribes of animals; but artificial, that is, constructed language, is a wholly different thing, although it may incorporate into itself features from natural language. The parrot is indeed said to talk, but it is sheer imitation; and he never originates any language.